Brain size in birds is related to traffic accidents.

Anders Pape Møller,Johannes Erritzøe

doi:10.1098/rsos.161040

Abstract

Estimates suggest that perhaps a quarter of a billion birds are killed by traffic annually across the world. This is surprising because birds have been shown to learn speed limits. Birds have also been shown to adapt to the direction of traffic and lane use, and this apparently results in reduced risks of fatal traffic accidents. Such behavioural differences suggest that individual birds that are not killed in traffic should have larger brains for their body size. We analysed the link between being killed by traffic and relative brain mass in 3521 birds belonging to 251 species brought to a taxidermist. Birds that were killed in traffic indeed had relatively smaller brains, while there was no similar difference for liver mass, heart mass or lung mass. These findings suggest that birds learn the behaviour of car drivers, and that they use their brains to adjust behaviour in an attempt to avoid mortality caused by rapidly and predictably moving objects.

Highlights

An extensive review of the literature on road casualties revealed effects of location, survey method, year and season on the number of traffic casualties [1]
The proportion of individual birds killed by traffic decreased from 60% to 0% across the range of relative brain sizes recorded
Box plots of residual brain size for birds that had been killed by traffic or those that died from other causes showed a larger top quartile for individual birds that had been killed by traffic than for those that died from other causes

Summary

Introduction

An extensive review of the literature on road casualties revealed effects of location, survey method, year and season on the number of traffic casualties [1]. Abundance was the single most important predictor of the frequency of traffic casualties in birds [2]. Some studies have shown that risk-taking behaviour and sociality may account for residual variation in the risk of traffic casualties [2]. This implies that there may have been response to selection linked to micro-evolutionary changes in escape behaviour [3] and the risk of traffic accidents

Methods

Results

Conclusion